[RFC PATCH 4/5] drm/ttm: Document and optimize ttm_bo_pipeline_gutting()
Christian König
christian.koenig at amd.com
Fri May 21 08:21:18 UTC 2021
Am 20.05.21 um 17:09 schrieb Thomas Hellström:
> If the bo is idle when calling ttm_bo_pipeline_gutting(), we unnecessarily
> create a ghost object and push it out to delayed destroy.
> Fix this by adding a path for idle, and document the function.
>
> Also avoid having the bo end up in a bad state vulnerable to user-space
> triggered kernel BUGs if the call to ttm_tt_create() fails.
>
> Finally reuse ttm_bo_pipeline_gutting() in ttm_bo_evict().
>
> Cc: Christian König <christian.koenig at amd.com>
> Signed-off-by: Thomas Hellström <thomas.hellstrom at linux.intel.com>
> ---
> drivers/gpu/drm/ttm/ttm_bo.c | 20 +++++-----
> drivers/gpu/drm/ttm/ttm_bo_util.c | 63 ++++++++++++++++++++++++-------
> drivers/gpu/drm/ttm/ttm_tt.c | 5 +++
> include/drm/ttm/ttm_tt.h | 10 +++++
> 4 files changed, 75 insertions(+), 23 deletions(-)
>
> diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
> index ca1b098b6a56..a8fa3375b8aa 100644
> --- a/drivers/gpu/drm/ttm/ttm_bo.c
> +++ b/drivers/gpu/drm/ttm/ttm_bo.c
> @@ -501,10 +501,15 @@ static int ttm_bo_evict(struct ttm_buffer_object *bo,
> bdev->funcs->evict_flags(bo, &placement);
>
> if (!placement.num_placement && !placement.num_busy_placement) {
> - ttm_bo_wait(bo, false, false);
> + ret = ttm_bo_wait(bo, true, false);
> + if (ret)
> + return ret;
>
> - ttm_bo_cleanup_memtype_use(bo);
> - return ttm_tt_create(bo, false);
> + /*
> + * Since we've already synced, this frees backing store
> + * immediately.
> + */
> + return ttm_bo_pipeline_gutting(bo);
Yeah, we tried to avoid pipeline_gutting here because of eviction. But I
think when you wait before that should work.
> }
>
> ret = ttm_bo_mem_space(bo, &placement, &evict_mem, ctx);
> @@ -974,13 +979,8 @@ int ttm_bo_validate(struct ttm_buffer_object *bo,
> /*
> * Remove the backing store if no placement is given.
> */
> - if (!placement->num_placement && !placement->num_busy_placement) {
> - ret = ttm_bo_pipeline_gutting(bo);
> - if (ret)
> - return ret;
> -
> - return ttm_tt_create(bo, false);
> - }
> + if (!placement->num_placement && !placement->num_busy_placement)
> + return ttm_bo_pipeline_gutting(bo);
>
> /*
> * Check whether we need to move buffer.
> diff --git a/drivers/gpu/drm/ttm/ttm_bo_util.c b/drivers/gpu/drm/ttm/ttm_bo_util.c
> index 919ee03f7eb3..1860e2e7563f 100644
> --- a/drivers/gpu/drm/ttm/ttm_bo_util.c
> +++ b/drivers/gpu/drm/ttm/ttm_bo_util.c
> @@ -479,7 +479,8 @@ static void ttm_transfered_destroy(struct ttm_buffer_object *bo)
> */
>
> static int ttm_buffer_object_transfer(struct ttm_buffer_object *bo,
> - struct ttm_buffer_object **new_obj)
> + struct ttm_buffer_object **new_obj,
> + bool realloc_tt)
> {
> struct ttm_transfer_obj *fbo;
> int ret;
> @@ -493,6 +494,17 @@ static int ttm_buffer_object_transfer(struct ttm_buffer_object *bo,
> ttm_bo_get(bo);
> fbo->bo = bo;
>
> + if (realloc_tt) {
> + bo->ttm = NULL;
> + ret = ttm_tt_create(bo, true);
> + if (ret) {
> + bo->ttm = fbo->base.ttm;
> + kfree(fbo);
> + ttm_bo_put(bo);
> + return ret;
> + }
> + }
> +
Can't we keep that logic in the caller? I think that would be cleaner.
> /**
> * Fix up members that we shouldn't copy directly:
> * TODO: Explicit member copy would probably be better here.
> @@ -763,7 +775,7 @@ static int ttm_bo_move_to_ghost(struct ttm_buffer_object *bo,
> dma_fence_put(bo->moving);
> bo->moving = dma_fence_get(fence);
>
> - ret = ttm_buffer_object_transfer(bo, &ghost_obj);
> + ret = ttm_buffer_object_transfer(bo, &ghost_obj, false);
> if (ret)
> return ret;
>
> @@ -836,26 +848,51 @@ int ttm_bo_move_accel_cleanup(struct ttm_buffer_object *bo,
> }
> EXPORT_SYMBOL(ttm_bo_move_accel_cleanup);
>
> +/**
> + * ttm_bo_pipeline_gutting - purge the contents of a bo
> + * @bo: The buffer object
> + *
> + * Purge the contents of a bo, async if the bo is not idle.
> + * After a successful call, the bo is left unpopulated in
> + * system placement. The function may wait uninterruptible
> + * for idle on OOM.
> + *
> + * Return: 0 if successful, negative error code on failure.
> + */
> int ttm_bo_pipeline_gutting(struct ttm_buffer_object *bo)
> {
> static const struct ttm_place sys_mem = { .mem_type = TTM_PL_SYSTEM };
> struct ttm_buffer_object *ghost;
> int ret;
>
> - ret = ttm_buffer_object_transfer(bo, &ghost);
> - if (ret)
> - return ret;
> + /* If already idle, no need for ghost object dance. */
> + ret = ttm_bo_wait(bo, false, true);
> + if (ret == -EBUSY) {
> + ret = ttm_buffer_object_transfer(bo, &ghost, true);
> + if (ret)
> + return ret;
When this is a shortcout to avoid work we should rather use the inverse
notation.
In other words something like that:
if (ret != -EBUSY) {
ttm_resource_free(bo, &bo->mem);
ttm_resource_alloc(bo, &sys_mem, &bo->mem);
ttm_tt_create()...
return ret;
}
>
> - ret = dma_resv_copy_fences(&ghost->base._resv, bo->base.resv);
> - /* Last resort, wait for the BO to be idle when we are OOM */
> - if (ret)
> - ttm_bo_wait(bo, false, false);
> + ret = dma_resv_copy_fences(&ghost->base._resv, bo->base.resv);
> + /* Last resort, wait for the BO to be idle when we are OOM */
> + if (ret)
> + ttm_bo_wait(bo, false, false);
>
> - ttm_resource_alloc(bo, &sys_mem, &bo->mem);
> - bo->ttm = NULL;
> + dma_resv_unlock(&ghost->base._resv);
> + ttm_bo_put(ghost);
> + } else {
> + if (!bo->ttm) {
> + ret = ttm_tt_create(bo, true);
> + if (ret)
> + return ret;
> + } else {
> + ttm_tt_unpopulate(bo->bdev, bo->ttm);
> + if (bo->type == ttm_bo_type_device)
> + ttm_tt_mark_for_clear(bo->ttm);
That's not legal, you can't unpopulate it when the BO is busy.
Instead the TT object must be destroyed with the ghost and a new one
created.
Christian.
> + }
> + ttm_resource_free(bo, &bo->mem);
> + }
>
> - dma_resv_unlock(&ghost->base._resv);
> - ttm_bo_put(ghost);
> + ttm_resource_alloc(bo, &sys_mem, &bo->mem);
>
> return 0;
> }
> diff --git a/drivers/gpu/drm/ttm/ttm_tt.c b/drivers/gpu/drm/ttm/ttm_tt.c
> index 539e0232cb3b..0b1053e93db2 100644
> --- a/drivers/gpu/drm/ttm/ttm_tt.c
> +++ b/drivers/gpu/drm/ttm/ttm_tt.c
> @@ -134,6 +134,11 @@ void ttm_tt_destroy_common(struct ttm_device *bdev, struct ttm_tt *ttm)
> }
> EXPORT_SYMBOL(ttm_tt_destroy_common);
>
> +void ttm_tt_mark_for_clear(struct ttm_tt *ttm)
> +{
> + ttm->page_flags |= TTM_PAGE_FLAG_ZERO_ALLOC;
> +}
> +
> void ttm_tt_destroy(struct ttm_device *bdev, struct ttm_tt *ttm)
> {
> bdev->funcs->ttm_tt_destroy(bdev, ttm);
> diff --git a/include/drm/ttm/ttm_tt.h b/include/drm/ttm/ttm_tt.h
> index 134d09ef7766..91552c83ac79 100644
> --- a/include/drm/ttm/ttm_tt.h
> +++ b/include/drm/ttm/ttm_tt.h
> @@ -157,6 +157,16 @@ int ttm_tt_populate(struct ttm_device *bdev, struct ttm_tt *ttm, struct ttm_oper
> */
> void ttm_tt_unpopulate(struct ttm_device *bdev, struct ttm_tt *ttm);
>
> +/**
> + * ttm_tt_mark_for_clear - Mark pages for clearing on populate.
> + *
> + * @ttm: Pointer to the ttm_tt structure
> + *
> + * Marks pages for clearing so that the next time the page vector is
> + * populated, the pages will be cleared.
> + */
> +void ttm_tt_mark_for_clear(struct ttm_tt *ttm);
> +
> void ttm_tt_mgr_init(unsigned long num_pages, unsigned long num_dma32_pages);
>
> #if IS_ENABLED(CONFIG_AGP)
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